1. Field of the Invention
The present invention describes a process for preparing polyester polyols of polyhydric alcohols by mono- or polyesterification of a dicarboxylic acid and/or an anhydride of a dicarboxylic acid with the corresponding polyhydric alcohols, optionally in a solvent and optionally with the addition of an acidic catalyst, while removing the water of reaction.
2. Description of the Background
Polyhydric alcohols are those compounds which have more than one hydroxyl group, for example from 2 to 6, preferably from 2 to 4, preferably 2 or 3.
Such polyester polyols serve as a precursor for polyurethanes, polyester resins and polyacrylates and are thus used in numerous applications.
These applications require in particular products which are very weakly colored, if at all, and have no inherent odor and high storage stability.
The preparation of polyester polyols from polyhydric alcohols and dicarboxylic acids with the exclusion of water is generally known.
The reactions conventionally take place with catalysis, for example with an acid, or merely by increasing the temperature, with or without vacuum treatment.
Since the polyester polyols of polyhydric alcohols generally cannot be distillatively purified owing to their high boiling points, by-products remain in the target ester and influence the further processing and/or quality both of the target ester and also of the subsequent products.